Silicone in water emulsions can be produced by emulsion polymerisation or by mechanical emulsification of a silicone polymer with one or more surfactants and water. Because silicones are highly hydrophobic, stable emulsions are difficult to produce mechanically and it is generally necessary to mix the silicone with a surfactant and a small amount of water under high mechanical shear to form a non-Newtonian “thick phase”, which has a very high viscosity at low shear rates (much more viscous at low shear rate than the silicone polymer alone) and often exhibits a yield stress (viscoplastic behaviour). The resulting emulsion can be diluted with further water and surfactant. The highly viscous nature of this “thick phase” emulsion leads to a risk of uneven mixing or localised overheating when the process is carried out batchwise on an industrial scale.
U.S. Pat. No. 5,504,150 describes preparing emulsions by mixing organosilicon compounds, with a condensation catalyst and with a pressurized gas to cause foaming, feeding the foaming mixture down a reactor chamber, forming liquid polymers in the chamber by allowing the compounds to polymerise in the chamber. After polymerising the compounds, water and a surfactant are fed to the chamber and mixed with the foam in the chamber to form a water-in-oil emulsion containing the polymers. The emulsion is collected at the outlet of the reactor and inverted by shearing to an oil-in-water emulsion.
U.S. Pat. No. 5,806,975 describes a method of continuous emulsification of high viscosity organopolysiloxane gums in a compounding extruder. JP-A-12-449 describes the continuous production of an organopolysiloxane grease by feeding an organopolysiloxane with 0.1 to 100% emulsifier and 0.5 to 20% water to a rotary disc mixer.
EP-A-874017 describes a method of making a silicone in water emulsion comprising mixing materials comprising (I) a composition containing at least one polysiloxane, at least one organosilicon material that reacts with said polysiloxane by a chain extension reaction and a metal containing catalyst for said chain extension reaction, (II) at least one surfactant and (III) water to form a mixture; and emulsifying the mixture.
EP-A-915122 describes a process for preparing a silicone latex. The process comprises forming a premix of polydiorganosiloxane and crosslinker and then forming silicone latex by mixing surfactant and water with the premix. A process for the continuous preparation of the silicone latex using in-line dynamic mixers is also described.